Suppression of lymphokine production by macrophages infiltrating murine virus-induced tumors

Immune spleen cells from mice injected with murine sarcoma virus (MSV) can produced migration inhibition factor (MIF) in vitro after stimulation with intact tumor cells. We have now found that this effector function can be regulated by suppressor macrophages present in the tumor. The cells from the tumor (CfT) exert a strong suppressive effect even after treatment with anti-Thy 1.2 plus complement but lose this capacity if adherent or phagocytic cells are removed, suggesting that the macrophage is the suppressor cell. The effects of the suppressor cells were exerted on a proliferation-independent function of the lymphocytes, since MIF production, as well as its suppression, occurred even after proliferation of the lymphocytes was blocked by mitomycin-C. The implications of these findings are that macrophages can suppress some early events involved in the activation of lymphocytes by antigen and that they do so through a mechanism that does not relate to the proliferation of the cells.